Thermal ink-jet printers employ a number of resistor elements to expel droplets of ink through a plurality of associated nozzles. Each resistor element is located in a chamber which is filled with ink supplied from an ink reservoir. A nozzle plate, having a plurality of nozzles, or openings, defines one side of the chamber. Each nozzle is associated with a resistor element. Upon energizing a particular element, a droplet of ink is expelled through the nozzle associated with that element toward the print medium. A microprocessor controls the firing of the ink droplets by sending electrical signals via conductive traces to the resistor elements. In this way, alphanumeric and other characters are formed on the print medium.
The tolerances of the nozzles are typically 40 to 60 .mu.m, and it is important that the ink does not clog them. In addition, the resistor elements can be fouled by repeated firings, but they must stand up to 50 million firings over the life of the cartridge for the system to be commercially practical.
In addition, consideration must be given to the interaction of the ink and the print medium. Since printing inks for use with ink-jet printers are usually aqueous solutions and the print medium is usually paper, the art continues to seek compounds that will assist in chemically or physically binding the dye molecule to the paper.
Inks which possess one or more of these desirable properties are known, but there are very few which possess all. Often, an improvement in one property results in degradation of another. Many commercially used inks represent a compromise in an attempt to achieve a satisfactory level of the various properties. Consequently, with these considerations plus the primary need to obtain a good print, materials which are added to ink-jet inks must be selected with great care.